.alpha.-fetoprotein is a major protein present in fetal serum. It is produced by the liver of fetal mammals as well as in the yolk sac. It is normally not present in children. Its appearance in the sera of children and adults is associated with hepatoma and yolk sac tumor, since these tumors specifically produce .alpha.-fetoprotein. The highly specific association of .alpha.-fetoprotein with such malignancies has attracted much interested.
The structure of .alpha.-fetoprotein, its genetic composition and the mechanism by which its genetic composition can be regulated has been extensively studied. DNA sequences complimentary to the mRNA sequence of .alpha.-fetoprotein have been cloned and the nucleotide sequences of the mRNAs and the amino acid sequences of the .alpha.-fetoprotein have been determined for the mouse (S&gt;W&gt;Law et al, Nature 291: 201-205) (1981); for the rat- L. L. Jagodzinski et al, Proc. Natl. Acad. Sci. 78: 3521-3525 (1981); and for humans-T. Morinaga et al Proc. Natl. Acad. Sci. 80: 4604-4608 (1983). The expression of rat .alpha.-fetoprotein cDNA in Escherichia coli and in yeast has also been reported in J. Biochem, 104, 968-972 (1988).
R. Boismenu et al, Life Sciences 43: 673-681 (1988) discloses the fusion of a mouse .alpha.-fetoprotein fragment of amino acid 256 to 548 with a portion of .beta.-galactosidase in E. coli to provide a protein immunoreactive with anti-mouse .alpha.-fetoprotein anti-serum. T. Morinaga has also described human .alpha.-fetoprotein with a signal peptide of 19 amino acids and a mature human .alpha.-fetoprotein composed of 590 amino acids.